Heretofore, as shown in FIG. 1, a general configuration of a motor control section of an electric power steering apparatus is such a configuration that, based on a deviation Δi(t) between a current command value calculated by such as a steering torque and a velocity and a motor current detection value that is fed back, a voltage command value is calculated by means of a control section 1 such as a proportional (P) control, a proportional-integral (PI) control, or a proportional-integral-differential (PID) control, and in accordance with the calculated voltage command value, a motor 20 is driven through an inverter. Electric power is supplied from a battery 14 to the inverter 2 through a power relay 13. However, in such a control system, since trying not to output influences of detection disturbances of the motor current detection value, it is impossible to enhance a control response very much, and a limitation is imposed on suppression of parameter variations of the motor 20 and an ECU (Electronic Control Unit) and disturbances of a motor input voltage. Therefore, in order to obtain a highly-robust control method with high response while suppressing the influences of the detection disturbances of the motor current detection value, in general, a method that mitigates influences of current detection noises to some extent by setting the current detection value used in current control as an estimation current and thereby enhances a response of the current control and improves operation sound performance and torque ripple performance, is thought about.
In Patent Document 1, a method and an apparatus that inputs dq-axis voltage command values of a vector control, calculates dq-axis estimation currents by means of a dq-axis current observer and performs a feedback control, are disclosed. In the method and the apparatus, a scheme that enhances robustness by making each parameter of a current observer model dependent on temperature detection value of each element and varying, is proposed. Further, in Patent Document 2, a motor control apparatus that estimates a motor current vale after several samples based on a voltage command value, a motor current detection value and input estimation disturbances of a motor that is estimated by a disturbance observer, uses the motor current-estimate value in control, and a current observer corresponds to a variation in the model parameters by a state feedback, is proposed.